Key Idea: Five categories: additive, subtractive (wasting), forming, joining, finishing. Place any process by asking what happens to the amount of material. Every process is a bargain between tooling cost and cost per part, and volume is what settles it. Additive builds layer by layer, so the layer height sets the surface, the orientation sets the strength, and overhangs set the support. 4D printing adds a stimulus; 5D printing adds two rotations so layers follow the curve. Joining is decided by one question: does it ever need to come apart? Finishing is decided by where the finish sits, which is what predicts how it fails. No real product uses one process, so every answer is a sequence with a reason at each step.
Paper 1 — multiple choice
- Place a named process in its category
- Identify a process from a description of what moves
- Choose the process suited to a shape and a volume
- Match a finish to a material
Paper 2 — analysing a product
- Explain why each technique was used on a component
- Justify one process against a named alternative
- Explain the sequence of processes in a product
- Evaluate the environmental cost of a manufacturing choice
Carried into the design project
- Criterion D — your prototype's process must be justified
- Criterion E — waste, tooling and end-of-life all sit here
- Print for learning; specify a real process for the product
The five categories are not a list to memorise. They are a test, and it works on an unfamiliar process as well as a familiar one.
| Ask | Category | Processes |
|---|---|---|
| Is there MORE material at the end? | Additive | FDM, SLA, SLS, PBF, LOM, material extrusion |
| Is there LESS? | Subtractive (wasting) | Cutting, milling, turning, abrading, laser and water jet |
| The SAME amount, in a new shape? | Forming | Bending, press forming, casting, injection, extrusion, rotational, blow, vacuum |
| Have separate pieces become ONE? | Joining | Adhering, fastening, stitching, weaving, welding |
| Has only the SURFACE changed? | Finishing | Anodising, plating, galvanising, powder coating, polishing, oils and waxes |
Each category drawn as what happens to the material.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Important: Swapping milling and turning. In turning the WORK spins, which is why it makes round shapes only. Recommending injection moulding for 300 parts. It needs tens of thousands to pay for the tool. Naming a process with no reason. Every mark is a pairing — process plus a property, volume, tolerance, cost or environment. Choosing a finish without the material. Anodising is for aluminium, galvanising for steel, oil for timber.
| Volume | What suits it | Why |
|---|---|---|
| One-off | Machining, bending, printing, hand assembly | No tooling to pay for at all, and a designer's time is the only real cost |
| Tens to hundreds | Vacuum forming, rotational moulding, printing, casting in sand | Cheap tooling that pays off in dozens; slow cycles do not matter at this volume |
| Thousands | Printing for complicated parts, pressing for simple ones | The crossover region, where the answer genuinely depends on the shape |
| Tens of thousands upwards | Injection moulding, press forming, extrusion, die casting | Expensive precision tooling spread across a huge run, and seconds per part |
Eight forming processes, each drawn as the tool that makes the shape.
🔒 Interactive diagram
Explore the labelled diagram, charts and maps for this topic in study mode.
Turning: the work spins. Milling: the tool spins. The powder bed is the support — which is why SLS and PBF need no support structures. Only fastening is genuinely temporary, and a glued product is one object at end of life. Zinc protects sacrificially; anodising is grown into the metal and cannot peel. Constant cross-section means extrusion. Large, hollow and seamless means rotational moulding.
A bicycle helmet has an expanded polystyrene liner, a thin polycarbonate outer shell, a woven strap and an adjustable polymer cradle. Explain the manufacturing technique used for each and why.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A furniture company proposes to 3D print the joints of a flat-pack chair instead of injection moulding them, for a run of 2,000 chairs a year. Evaluate the proposal.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
A garden tool has a powder-coated steel shaft. Justify this finish, and say when it would be the wrong choice.
🔒 Model answer plan
See the mark-by-mark plan — for / against / judgement, with marking guidance — in study mode.
What separates milling from turning?
Why do SLS and powder bed fusion need no supports?
Which forming process for a large seamless hollow part?
What is the first question about any joint?
Why does where a finish sits matter?
What makes a "why this process" answer complete?
Exam tips
- Place a process by what happens to the amount of material, then name the reason it was chosen.
- Say the volume in any cost argument: cheap at what volume, and cheaper than what?
- For subtractive, say which part rotates. For additive, name orientation, layer height or support.
- For a joint, answer can it come apart before anything else.
- For a finish, match the material and the environment, and say how it will fail.
- Work a product through in order — shape, size, joining, surface — with a reason at every stage.